Light storage integrated synchronous generator, power generation system and light storage combined control method

Abstract

The invention provides a light storage integrated synchronous generator. The light storage integrated synchronous generator mainly comprises a photovoltaic MPPT tracker, an energy storage battery, a light storage converter, a coordination controller and a boosting transformer. The photovoltaic MPPT tracker is used for connecting the photovoltaic string to the direct current bus, so that the photovoltaic string works at the maximum power; the energy storage battery is directly connected to the direct current bus; the optical storage converter is used for realizing three-way energy conversion and voltage source type active support control among the photovoltaic MPPT tracker, the energy storage battery and the alternating current power grid; the boosting transformer is used for connecting the optical storage converter to an alternating current power grid; and the coordination controller receives a dispatching instruction of a station control layer upwards, controls the optical storage converter and the photovoltaic MPPT tracker downwards, and controls optical storage combined grid connection according to different dispatching instructions. The invention also discloses an optical storage integrated synchronous power generation system and an optical storage combined control method. The optical storage converter simulates the rotor motion of the synchronous generator, and the energy for maintaining the rotational inertia of the rotor is provided by the energy storage battery.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic power generation grid connection technology, and particularly relates to a photovoltaic-storage integrated synchronous generator, power generation system and photovoltaic-storage joint control method. Background Technology

[0002] Traditional thermal and hydroelectric power plants generate alternating current (AC) through rotating motors at the head of the plant. The current waveform is smooth and continuous, and no harmonics occur when the power plants are connected to the AC grid. Furthermore, the rotation of the motor rotor has inertia and damping, which provides active support against momentary grid faults.

[0003] Solar power generation produces direct current (DC) electricity, which is then connected to the grid using inverters composed of power electronic devices. Solar power generation suffers from volatility, randomness, and intermittency, and also generates harmonics. Therefore, when connected to the AC grid, it can impact the stability and security of the power grid.

[0004] On the other hand, the AC waveform generated by the grid-connected inverter has almost no rotational inertia and damping. As the proportion of solar power generation in the grid gradually increases, the inertial constant of the grid continues to decrease, the grid's ability to actively support frequency deficits and voltage fluctuations decreases, and the grid's security is reduced.

[0005] Existing technologies propose introducing the operating characteristics of a virtual synchronous generator (VSG) into the control strategy of grid-connected inverters or energy storage converters to provide a certain amount of rotational inertia to the power grid.

[0006] Early current-controlled inverters relied on the existing power grid, and their support for the grid was essentially passive, making it difficult to effectively improve the stability of photovoltaic power generation grid connection under weak power grid conditions.

[0007] However, the actively supported energy storage converter proposed later is prone to overcurrent during fault ride-through and has low reactive power control accuracy.

[0008] Meanwhile, both current-controlled inverters and active-supported energy storage converters can achieve certain frequency and voltage stability functions when designed according to the "virtual synchronization" control strategy. However, due to limitations in topology, equipment overload capacity, and control strategy, they all suffer from slow response speed and poor regulation accuracy. Summary of the Invention

[0009] To address the aforementioned issues, this disclosure provides an integrated photovoltaic-storage synchronous generator, a power generation system, and a combined photovoltaic-storage control method. The method employs a voltage-source controlled photovoltaic-storage converter to simulate the rotor motion equation of the synchronous generator. The energy maintaining the rotor's rotational inertia is provided by the energy storage battery, which is directly connected to the DC bus, thereby improving the response speed of the integrated photovoltaic-storage synchronous generator in supporting transient voltages in the power grid.

[0010] This invention provides a photovoltaic-storage integrated synchronous generator, mainly comprising a photovoltaic MPPT tracker, an energy storage battery, a photovoltaic-storage converter, a coordination controller, and a step-up transformer. The photovoltaic MPPT tracker is used to connect the photovoltaic string to the DC bus, enabling the photovoltaic string to operate at maximum power. The energy storage battery is directly connected to the DC bus. The photovoltaic-storage converter is used to realize three-way energy conversion and voltage source-type active support control between the photovoltaic MPPT tracker, the energy storage battery, and the AC grid. The step-up transformer is used to connect the photovoltaic-storage converter to the AC grid. The coordination controller receives dispatch instructions from the station control layer and controls the photovoltaic-storage converter and photovoltaic MPPT, controlling the joint grid connection of photovoltaic and energy storage according to different dispatch instructions.

[0011] Furthermore, a current transformer and a voltage transformer are installed between the photovoltaic-storage converter and the step-up transformer to collect the output current and voltage signals of the photovoltaic-storage converter and transmit them to the coordination controller.

[0012] Furthermore, the coordinating controller is simultaneously connected to the energy storage battery, the photovoltaic MPPT tracker, and the photovoltaic-energy storage converter. It determines whether the energy storage system is ready for charging / discharging based on the state of charge of the energy storage battery, and utilizes the power difference between the photovoltaic DC side power and the AC grid connection point to achieve charging / discharging control of the energy storage battery.

[0013] Furthermore, the coordinating controller collects real-time output data from the photovoltaic-storage converter, the photovoltaic MPPT tracker, the energy storage battery, and the low-voltage side power output data of the step-up transformer, and uploads it to the monitoring system.

[0014] Furthermore, the rotor equation of the synchronous generator is:

[0015]

[0016] Where Tm and Te are the mechanical torque and electromagnetic torque of the synchronous generator, respectively, in N·m; ω and ω0 are the actual angular velocity of the power grid and the synchronous angular velocity, respectively, in rad / s; D is the damping coefficient, in N·m·s / rad; Pm is the mechanical power of the synchronous motor, Pe is the electromagnetic power of the synchronous motor; J is the moment of inertia, in kg·m2; and δ is the output power angle, in rad.

[0017] Furthermore, the photovoltaic-storage converter adopts a voltage source control strategy, and the mathematical models used for the active and reactive power loops are as follows:

[0018]

[0019]

[0020] 0 = jodt(3)

[0021] In the formula, P* and Q* are the reference values ​​of the output active and reactive power, respectively; P and Q are the feedback values ​​of the output active and reactive power, respectively; Dp is the damping coefficient; Dq is the reactive-voltage droop coefficient; ω* and ω are the rated and actual values ​​of the grid electrical angular velocity, respectively; J is the virtual moment of inertia; K is the inertia coefficient of the simulated excitation regulation; Ug* and Ug are the rated and feedback values ​​of the grid voltage amplitude, respectively; E and θ are the amplitude and phase of the output potential, respectively.

[0022] This invention also discloses a photovoltaic-storage integrated synchronous power generation system, comprising at least two of the aforementioned photovoltaic-storage integrated synchronous generators; each photovoltaic-storage integrated synchronous generator includes an energy storage battery, a photovoltaic-storage converter, a coordination controller, and several photovoltaic MPPT trackers; each photovoltaic MPPT tracker is connected to at least one photovoltaic string; the photovoltaic-storage integrated synchronous generator system further includes a station control layer monitoring system, a fast power control system, and a cluster coordination control system; the monitoring system, fast power control system, and cluster coordination control system are respectively connected to the coordination controller of each photovoltaic-storage integrated synchronous generator.

[0023] Furthermore, the monitoring system includes an automatic power generation control system and an automatic voltage control system.

[0024] This invention also provides a photovoltaic-storage integrated grid-connected control method, applied to the aforementioned photovoltaic-storage integrated synchronous power generation system. The method uses a voltage-source controlled photovoltaic-storage converter to simulate the rotor motion equation of a synchronous generator, and the energy to maintain the rotor's rotational inertia is provided by a storage battery directly connected to the DC bus.

[0025] Furthermore, the coordinating controller is connected to the station control layer's monitoring system, fast power control system, and cluster coordination control system; the coordinating controller selects remote mode or local mode operation according to the instructions of the monitoring system.

[0026] Compared with the prior art, this disclosure has the following advantages:

[0027] This system employs a voltage-source controlled integrated photovoltaic-storage synchronous generator. The photovoltaic strings are connected to the DC / DC converter via MPPT trackers, with the number of trackers configured according to actual project requirements to meet different photovoltaic capacity ratios. The energy storage battery system is directly connected to the photovoltaic DC bus without the need for a DC-DC converter. It boasts advantages such as high equipment integration, high system conversion efficiency, unified communication protocol, rapid response of photovoltaic-storage coordinated control, and high power control accuracy.

[0028] Because the photovoltaic-storage converter simulates the motion of a conventional synchronous rotor, the rotor inertia and damping characteristics of the virtual synchronous generator (VSG), reflected in the rotor motion equations, can provide inertial support for the grid after grid system disturbances. Furthermore, by adding primary frequency regulation control and voltage regulation control, the external characteristics of the photovoltaic-storage integrated synchronous generator can be made closer to those of a conventional synchronous generator. The energy required to maintain the external characteristics of the synchronous generator is provided by the energy storage battery. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A schematic diagram of the topology of a photovoltaic-storage integrated synchronous power generation system according to an embodiment of the present invention is shown;

[0031] Figure 2 The equivalent circuit of a voltage source type photovoltaic energy storage converter is shown;

[0032] Figure 3 The basic topology diagram of the voltage source type photovoltaic energy storage converter is shown.

[0033] Figure 1 Explanation of Chinese symbols:

[0034] CT & PT: Current transformer and voltage transformer; T: Step-up transformer; I, II: Photovoltaic-storage integrated synchronous generator. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Figure 1 An integrated photovoltaic-storage synchronous power generation system according to an embodiment of the present disclosure is shown, comprising at least two integrated photovoltaic-storage synchronous generators I and II.

[0037] The photovoltaic-storage integrated synchronous generator mainly consists of five core components: a photovoltaic MPPT tracker, an energy storage battery, a photovoltaic-storage converter, a coordination controller, and a step-up transformer.

[0038] A photovoltaic MPPT tracker is a photovoltaic DC / DC converter that uses MPPT (Maximum Power Point Tracking) control to connect photovoltaic strings to a DC bus, enabling the photovoltaic strings to operate at maximum power.

[0039] The energy storage battery is directly connected to the DC bus. Compared with existing technologies, the energy storage battery in this embodiment eliminates the need for an energy storage DC-DC converter (energy storage DC / DC), improving the response speed of the energy storage battery to grid reactive power regulation. The charging and discharging of the energy storage battery adopts indirect control, that is, the charging and discharging of the energy storage battery is controlled by the power difference between the photovoltaic DC-side power and the AC grid connection point. The control logic is simple, and the response speed reaches the millisecond level, which can meet the instantaneous response requirements of the photovoltaic-energy storage converter to achieve active support.

[0040] A photovoltaic-storage converter is a modular photovoltaic-storage DC / AC converter used to achieve three-way energy conversion between photovoltaic MPPTs, energy storage batteries, and the AC grid, replacing traditional photovoltaic inverters and energy storage converters. On the DC side, the photovoltaic strings are connected to the DC bus through the photovoltaic MPPT, and the energy storage batteries are directly connected to the DC bus. On the AC side, the photovoltaic-storage converter controls the AC power through grid connection, while supporting the stability of grid frequency and voltage according to a voltage source control strategy.

[0041] The step-up transformer raises the AC voltage of the photovoltaic-storage converter to 35kV, enabling the converter to connect to the AC power grid. The rated total capacity of the AC side of the photovoltaic-storage converter is consistent with the rated capacity of the matching step-up transformer.

[0042] The coordination controller receives dispatch instructions from the station control layer and controls the photovoltaic-storage converter and photovoltaic MPPT tracker. Based on different dispatch instructions, it controls the combined photovoltaic and storage grid connection, ensuring the safe, stable, efficient, and reliable operation of the integrated photovoltaic-storage synchronous generator while fully leveraging the reactive power regulation role of the energy storage battery in photovoltaic grid-connected power generation. The coordination controller collects real-time output data from the photovoltaic-storage converter, photovoltaic MPPT tracker, energy storage battery, low-voltage side power output data from the step-up transformer, metering and measuring instrument data, energy storage fire protection system data, and environmental control system data, and uploads this data to the monitoring system.

[0043] The active support function of the photovoltaic-storage integrated synchronous generator is realized by the photovoltaic-storage converter.

[0044] See appendix Figure 1In a photovoltaic-storage integrated synchronous generator, the output terminals of several photovoltaic MPPT trackers are connected in parallel to the DC bus; the energy storage battery is directly connected to the DC bus; the photovoltaic-storage converter is connected to the DC bus to convert DC power into AC power, which is then output through a step-up transformer; the coordination controller is simultaneously connected to the energy storage battery, the photovoltaic MPPT trackers, and the photovoltaic-storage converter, and determines whether the energy storage system has the conditions for charging / discharging based on the state of charge of the energy storage battery, and uses the power difference between the photovoltaic DC side power and the AC grid connection point to realize the charging and discharging control of the energy storage battery.

[0045] A voltage transformer is installed between the photovoltaic energy storage converter and the step-up transformer to collect the output voltage signal of the photovoltaic energy storage converter and transmit it to the coordination controller.

[0046] As a preferred option, at least one photovoltaic string is connected to each photovoltaic MPPT tracker.

[0047] The photovoltaic-storage integrated synchronous generator, which adopts voltage source control technology, introduces the rotor motion and generator state equations of a synchronous generator, and can simulate the amplitude and phase angle (power angle) of the internal potential of a conventional generator: by changing the power angle, the active power is changed, and by changing the voltage amplitude, the reactive power is changed, thus exhibiting the characteristics of a voltage source.

[0048] The voltage source photovoltaic-storage converter in this invention adopts a control strategy similar to that of a synchronous generator, and can achieve self-synchronization between the converter and the power grid without the need for a phase-locked loop. Its external characteristics are voltage source characteristics, and it can be equivalent to a circuit with a controllable voltage source series impedance.

[0049] Figure 2 The equivalent circuit of a voltage source type photovoltaic energy storage converter is shown in the figure. V PCC i is the voltage at the common coupling point (the output voltage of the photovoltaic MPPT port). PCC C is the current at the common coupling point (the output current of the photovoltaic MPPT port). v For the inner loop controller, E ＊ ω represents the voltage rating of the photovoltaic-storage integrated synchronous generator. * The frequency rating of the photovoltaic-storage integrated synchronous generator, V m δ is the reference amplitude of the voltage. m For reference angle of work, Z c For virtual impedance, PCC is the common coupling point, Z g This represents the line impedance.

[0050] The rotor equation of the virtual synchronous generator in this embodiment is:

[0051]

[0052] Among them, T m and Te ω and ω0 represent the mechanical torque and electromagnetic torque of the synchronous generator, respectively, in N·m; ω and ω0 represent the actual angular velocity of the power grid and the synchronous angular velocity, respectively, in rad / s; D is the damping coefficient, in N·m·s / rad; P m P represents the mechanical power of the synchronous motor. e J represents the electromagnetic power of the synchronous motor; J is the moment of inertia, in kg·m. 2 δ represents the output power angle, in rad.

[0053] Voltage source type photovoltaic energy storage converters require stable energy support for control and have a fast energy storage response speed, which can release energy instantly.

[0054] The photovoltaic-storage integrated synchronous generator of this invention adopts a photovoltaic-storage DC-coupled, AC-grid topology. The energy storage battery is directly connected to the DC side of the photovoltaic-storage converter via the DC bus without any conversion equipment, and can directly absorb electricity from the DC bus. When the photovoltaic-storage converter provides rotational inertia, the energy storage battery can directly provide energy as a stable energy source for voltage source control, so as to meet the instantaneous response requirements of the converter to achieve active support.

[0055] The joint operation control of the photovoltaic-storage integrated synchronous generator is achieved by a coordination controller.

[0056] The essence of voltage source type photovoltaic-storage converter control is to simulate the operating principle of AC voltage source by controlling the photovoltaic-storage converter, thereby obtaining operating characteristics similar to synchronous generator.

[0057] The basic topology of voltage source type photovoltaic-storage converter control is as follows: Figure 3 As shown. Figure 3 Middle,U dc e is the DC bus voltage; a e b e c These represent the three-phase output voltages of the inverter's AC side; L1, R1, R2, and C are the parameters of the LC filter; i ga i gb i gc These are the three-phase currents of the power grid; u ga u gb u gc These are the three-phase voltages of the power grid. Figure 3 The topology shown is based on existing technology.

[0058] The active and reactive power control loops of the voltage-source photovoltaic-storage converter control strategy essentially simulate the speed governor and excitation regulation functions of a synchronous generator, respectively. By controlling the grid frequency through the active power and the grid voltage through the reactive power of the synchronous generator, the voltage-source control strategy can achieve operating characteristics similar to a traditional synchronous generator, thus providing rotational inertia and damping support for the grid. The photovoltaic-storage converter based on voltage-source control can achieve primary frequency regulation and primary voltage regulation, ultimately making grid-connected energy storage equivalent to a synchronous generator. The mathematical models for the active and reactive power loops used in the voltage-source control strategy are as follows:

[0059]

[0060]

[0061] θ=∫ωdt (3)

[0062] In the formula, P ＊ and Q ＊ These are the reference values ​​for the output active and reactive power, respectively; P and Q are the feedback values ​​for the output active and reactive power, respectively; D p D is the damping coefficient; q ω is the reactive power-voltage droop coefficient. ＊ ω and ω are the rated and actual values ​​of the electrical angular velocity of the power grid, respectively; J is the virtual moment of inertia; K is the inertia coefficient of the simulated excitation regulation; U g ＊ and U g These are the rated and feedback values ​​of the grid voltage amplitude, respectively; E and θ are the amplitude and phase of the output potential, respectively.

[0063] The existence of the virtual rotational inertia J gives the control strategy of the voltage source type photovoltaic-storage converter inertia during power and frequency dynamic processes; while the damping coefficient D p This enables the control strategy of voltage source photovoltaic-storage converters to dampen power oscillations and respond to grid frequency changes.

[0064] By controlling the frequency of active power generation and the voltage of reactive power generation, a voltage-source photovoltaic-storage converter employing a virtual synchronous generator control strategy can achieve operating characteristics similar to a traditional synchronous generator, thus providing inertial and damping support for the power grid. Based on the voltage-source photovoltaic-storage converter control method, primary frequency and voltage regulation of the power grid can also be achieved. The back EMF generated by the virtual synchronous generator passes through a current loop, and the resulting modulated wave drives the photovoltaic-storage converter via a PWM module, making the photovoltaic-storage converter equivalent to a synchronous generator.

[0065] See appendix Figure 1This invention discloses a photovoltaic-storage integrated synchronous power generation system, in which the coordination controller is connected to a station control layer monitoring system (including an AGC / AVC system), a fast power control system, and a cluster coordination control system. The fast power control system employs a fast fiber optic communication module, achieving rapid control of numerous inverter units through a high-priority communication method that allows for one-to-many transmission and multiple-to-receive and requires no backhaul confirmation. The cluster coordination control system is used to achieve voltage coordination control of each photovoltaic-storage integrated generator.

[0066] Based on the above external controls, the coordination controller can select either remote or local mode. The specific control strategy is as follows:

[0067] 1. Receive remote control commands from the station control layer

[0068] 1) Integrated grid connection of photovoltaic and energy storage

[0069] The coordinating controller receives power commands from the station control layer AGC (Automatic Generation Control) system through the monitoring communication interface. Based on the active power value Pagc issued by the AGC system, the maximum active power Pmax at the low-voltage side grid connection point of the step-up transformer (e.g., 1.1 times the rated capacity of the step-up transformer), the real-time active power Ppcc at the low-voltage side grid connection point of the step-up transformer, the real-time active power Ppv of the photovoltaic string cluster, the chargeable active power Pcharge of the energy storage battery, the dischargeable active power Pdischarge of the energy storage battery, and the SOC (sustainable capacity) value of the energy storage battery, the photovoltaic MPPT tracker and the energy storage battery are adjusted in real time.

[0070] The real-time active power of the controlled photovoltaic string cluster is Ppv′, and the real-time active power of the low-voltage side grid connection point of the controlled step-up transformer is Ppcc′.

[0071] a) When Ppcc > Pagc and the energy storage battery is ready for charging (SOC < upper limit), control the energy storage battery to charge (absorb active power). When the energy storage battery is charged to the upper limit of SOC, the energy storage battery goes into standby mode. If the Pagc value does not change, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to limit the power generation (limit the power generation) so that Ppv′ = Ppcc′ = Pagc.

[0072] b) When Ppcc < Pagc and the energy storage battery is ready to discharge (SOC > lower limit), control the energy storage battery to discharge (release active power). When the energy storage battery is discharged to the lower limit of SOC, the energy storage battery will standby. If the Pagc value does not change, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to generate electricity at the current maximum power Ppvmax = Ppccmax (release active power).

[0073] c) When Pagc > Pmax, Pmax is used as the maximum power command limit to adjust the photovoltaic-storage converter, photovoltaic MPPT tracker and energy storage battery in real time.

[0074] 2) Peak shaving

[0075] The coordinating controller receives peak-shaving power commands from the station control layer through the monitoring communication interface. Based on the peak-shaving active power value Ptf, the maximum active power Pmax at the grid connection point on the low-voltage side of the step-up transformer (e.g., taking 1.1 times the rated capacity of the step-up transformer), the real-time active power Ppcc at the grid connection point on the low-voltage side of the step-up transformer, the real-time active power Ppv of the photovoltaic string cluster, the chargeable active power Pcharge of the energy storage battery, the dischargeable active power Pdischarge of the energy storage battery, and the SOC value of the energy storage battery, the photovoltaic MPPT tracker and the energy storage battery are adjusted in real time.

[0076] The real-time active power of the controlled photovoltaic string cluster is Ppv′, and the real-time active power of the low-voltage side grid connection point of the controlled step-up transformer is Ppcc′.

[0077] a) When Ppcc > Ptf and the energy storage battery is ready for charging (SOC < upper limit), control the energy storage battery to charge (absorb active power). When the energy storage battery is charged to the upper limit of SOC, the energy storage battery goes into standby mode. If the Ptf value does not change, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to limit the power generation (limit the power generation) so that Ppv′ = Ppcc′ = Ptf.

[0078] b) When Ppcc < Ptf and the energy storage battery is ready to discharge (SOC > lower limit), control the energy storage battery to discharge (release active power). When the energy storage battery is discharged to the lower limit of SOC, the energy storage battery will standby. If the Ptf value does not change, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to generate electricity at the current maximum power Ppvmax = Ppccmax (release active power).

[0079] c) When Ptf > Pmax, Pmax is used as the maximum power command limit to adjust the photovoltaic-storage converter, photovoltaic MPPT tracker and energy storage battery in real time.

[0080] 3) Voltage regulation

[0081] The coordinating controller receives AVC (Automatic Voltage Control) power commands from the station control layer through the monitoring communication interface. Based on the reactive power value Qavc issued by the AVC system, the maximum reactive power Qmax at the low-voltage side grid connection point of the step-up transformer (e.g., taking 1.1 times the rated capacity of the step-up transformer), the real-time reactive power Qpcc at the low-voltage side grid connection point of the step-up transformer, the real-time reactive power Qpv of the photovoltaic string cluster, the chargeable reactive power Qcharge of the energy storage battery, the dischargeable reactive power Qdischarge of the energy storage battery, and the SOC value of the energy storage battery, the controller adjusts the photovoltaic-storage converter, the photovoltaic MPPT tracker, and the energy storage battery in real time.

[0082] The real-time active power of the controlled photovoltaic string cluster is Ppv′, and the real-time active power of the low-voltage side grid connection point of the controlled step-up transformer is Ppcc′.

[0083] a) When Qpcc > Qavc and the energy storage battery is ready for charging (SOC < upper limit), control the energy storage battery to charge (absorb reactive power). When the energy storage battery is charged to the upper limit of SOC, the energy storage battery goes into standby mode. If the Qagc value does not change, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to limit power generation (limit reactive power generation) so that QPpv′ = Qpcc′ = Qavc.

[0084] b) When Qpcc < Qagc and the energy storage battery is ready to discharge (SOC > lower limit), control the energy storage battery to discharge (release reactive power). When the energy storage battery is discharged to the lower limit of SOC, the energy storage battery will standby. If the Qagc value remains unchanged, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to generate electricity at the current maximum power Qpvmax = Qpccmax (release reactive power).

[0085] c) When Qagc > Qmax, Qmax is used as the maximum power command limit to adjust the photovoltaic-storage converter, photovoltaic MPPT tracker and energy storage battery in real time.

[0086] 4) Primary frequency modulation

[0087] The coordinating controller receives power commands from the primary frequency regulation control system at the station control layer via a fast control communication interface (the primary frequency regulation control system collects grid-connected current and voltage in real time to calculate the frequency, and issues frequency regulation commands when the frequency regulation dead zone is exceeded). Based on the active power value Ptp issued by the primary frequency regulation, the maximum active power Pmax at the grid-connected point on the low-voltage side of the step-up transformer (for example, taking 1.1 times the rated capacity of the step-up transformer), the real-time active power Ppcc at the grid-connected point on the low-voltage side of the step-up transformer, the real-time active power Ppv of the photovoltaic string cluster, the chargeable active power Pcharge of the energy storage battery, the dischargeable active power Pdischarge of the energy storage battery, and the SOC value of the energy storage battery, the controller adjusts the photovoltaic-energy storage converter, the photovoltaic MPPT tracker, and the energy storage battery in real time.

[0088] The real-time active power of the controlled photovoltaic string cluster is Ppv′, and the real-time active power of the low-voltage side grid connection point of the controlled step-up transformer is Ppcc′.

[0089] a) When Ppcc > Ptp and the energy storage battery is ready for charging (SOC < upper limit), control the energy storage battery to charge (absorb active power). When the energy storage battery is charged to the upper limit of SOC, the energy storage battery goes into standby mode. If the Ptf value does not change, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to limit the power generation (limit the power generation) so that Ppv′ = Ppcc′ = Ptf.

[0090] b) When Ppcc < Ptp and the energy storage battery is ready to discharge (SOC > lower limit), control the energy storage battery to discharge (release active power). When the energy storage battery is discharged to the lower limit of SOC, the energy storage battery will standby. If the Ptf value does not change, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to generate electricity at the current maximum power Ppvmax = Ppccmax (release active power).

[0091] c) When Ptp > Pmax, Pmax is used as the maximum power command limit to adjust the photovoltaic-storage converter, photovoltaic MPPT tracker and energy storage battery in real time.

[0092] 2. Issue control commands locally

[0093] 1) Integrated grid connection of photovoltaic and energy storage

[0094] The coordinating controller automatically and dynamically sets the power control threshold of the photovoltaic-storage integrated synchronous generator grid connection point according to the collected photovoltaic power generation (determined by weather and irradiance) in three time periods each day (the number of time periods and the start and end times of the time periods can be set).

[0095] The coordinating controller dynamically sets the maximum output control threshold Pdtagc (Pdtagc≤Pmax) of the photovoltaic and energy storage power generation unit for each time period of the day based on the maximum active power Pmax of the low-voltage side grid connection point of the step-up transformer (e.g., taking 1.1 times the rated capacity of the step-up transformer), the real-time active power Ppcc of the low-voltage side grid connection point of the step-up transformer, the real-time active power Ppv of the photovoltaic string cluster, the chargeable active power Pcharge of the energy storage battery, the dischargeable active power Pdischarge of the energy storage battery, and the SOC value of the energy storage battery. It also adjusts the photovoltaic and energy storage converter, the photovoltaic MPPT tracker, and the energy storage battery in real time.

[0096] The real-time active power of the controlled photovoltaic string cluster is Ppv′, and the real-time active power of the low-voltage side grid connection point of the controlled step-up transformer is Ppcc′.

[0097] First period: Morning period 6:00-8:59 (period can be set). At 6:00 (settable), it is determined whether the photovoltaic string cluster power Ppv is greater than 10% of Pmax (settable). If so, 80% of Pmax (settable) is used as the output threshold Pdtagc for this period. Otherwise, 40% of Ppv at this moment (settable) is used as the threshold Pdtagc for this period.

[0098] a) When Ppcc > Pdtagc and the energy storage battery is ready for charging (SOC < upper limit), control the energy storage battery to charge (absorb active power). When the energy storage battery is charged to the upper limit of SOC, the energy storage battery goes into standby mode. If the value of Pdtagc does not change, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to limit the power generation (limit the power generation) so that Ppv′ = Ppcc′ = Pdtagc.

[0099] b) When Ppcc < Pdtagc and the energy storage battery is ready to discharge, control the energy storage battery to discharge (release active power). After the energy storage battery is discharged to the lower limit of the SOC setting, the energy storage battery goes into standby mode. If the Pdtagc value remains unchanged, control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to operate at the current maximum power.

[0100] Ppvmax = Ppccmax (power generation, release of active power).

[0101] The second time period is from 9:00 to 14:59 (the time period can be set). At 9:00 (the time period can be set), it is determined whether the photovoltaic string cluster power Ppv is greater than 100% Pmax (the time period can be set). If so, 100% Pma (the time period can be set) is used as the threshold Pdtggc for this time period. Otherwise, 80% of Ppv at this time (the time period can be set) is used as the threshold Pdtagc for this time period.

[0102] The control strategy is the same as in the first period.

[0103] The third time period: afternoon period 15:00-19:00 (time period can be set). At 15:00 (settable), it is determined whether the photovoltaic string cluster power Ppv is greater than 80% of Pmax (settable). If so, 60% of Pmax (settable) is used as the threshold Pdtggc for this time period. Otherwise, 40% of Ppv at this time (settable) is used as the threshold Pdtagc for this time period.

[0104] The control strategy is the same as in the first period.

[0105] 2) Primary frequency modulation

[0106] The coordinating controller calculates the grid connection frequency by collecting the current and voltage on the low-voltage side of the step-up transformer. Based on the fact that the current frequency exceeds the set dead zone range of the reference frequency (the parameter can be set), it calculates the active power deviation command Ptp. At the same time, based on the maximum active power Pmax of the grid connection point on the low-voltage side of the step-up transformer (for example, taking 1.1 times the rated capacity of the step-up transformer), the real-time active power Ppcc of the grid connection point on the low-voltage side of the step-up transformer, the real-time active power Ppv of the photovoltaic string cluster, the chargeable active power Pcharge of the energy storage battery, the dischargeable active power Pdischarge of the energy storage battery, and the SOC value of the energy storage battery, it adjusts the photovoltaic-energy storage converter, the photovoltaic MPPT tracker, and the energy storage battery in real time.

[0107] The real-time active power of the controlled photovoltaic string cluster is Ppv′, and the real-time active power of the low-voltage side grid connection point of the controlled step-up transformer is Ppcc′.

[0108] a) When the frequency at the grid connection point is lower than the reference frequency and the frequency deviation exceeds the dead zone, the local frequency adjustment command is to increase the frequency.

[0109] If Pdischarge > Ptp, control the energy storage battery to discharge at the difference between the two (release active power) so that Pdischarge′ = Ptp; if Pdischarge < Ptp, control the photovoltaic-energy storage converter, photovoltaic MPPT tracker and energy storage battery to discharge at the current maximum power Pdischargemax + Ppvmax = Ppccmax (release active power).

[0110] b) When the grid connection point frequency is higher than the reference frequency and the frequency deviation exceeds the dead zone, the local frequency modulation command is to lower the frequency.

[0111] If Pcharge > Ptp, control the energy storage battery to charge by the difference between the two (absorb active power), so that Pcharge′ = Ptp; if Pcharge < Ptp, control the energy storage battery to charge by the current maximum power Pchargemax (absorb active power), and at the same time control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to limit power generation (limit active power generation), so that Pchargemax + Ppv′ = Ptp.

[0112] 3) Voltage regulation

[0113] The coordinating controller collects the voltage on the low-voltage side of the step-up transformer and calculates the reactive power deviation command Qty based on the current voltage exceeding the set dead zone range of the reference voltage (parameter is configurable). Simultaneously, it adjusts the photovoltaic-storage converter, photovoltaic MPPT tracker, and battery in real time based on the maximum reactive power Qmax at the grid connection point on the low-voltage side of the step-up transformer (e.g., 1.1 times the rated capacity of the step-up transformer), the real-time reactive power Qpcc at the grid connection point on the low-voltage side of the step-up transformer, the real-time reactive power Qpv of the photovoltaic string cluster, the chargeable reactive power Qcharge of the energy storage battery, the dischargeable reactive power Qdischarge of the energy storage battery, and the SOC value of the energy storage.

[0114] After being controlled, the reactive power that the energy storage battery can discharge is Qdischarge′, the reactive power that the energy storage can charge is Qcharge′, and the real-time reactive power of the photovoltaic system after being controlled is Qpv′.

[0115] a) When the grid connection point voltage is lower than the reference voltage and the voltage deviation exceeds the dead zone, the local voltage regulation command is to increase the voltage.

[0116] If Qdischarge > Qty, control the energy storage battery to discharge at the difference between the two (release reactive power) so that Qdischarge′ = Qty; if Qdischarge < Qty, control the photovoltaic-energy storage converter, photovoltaic MPPT tracker and energy storage battery to discharge at the current maximum power Qdischargemax + Qpvmax = Qpccmax (release reactive power).

[0117] b) When the grid connection point voltage is higher than the reference voltage and the voltage deviation exceeds the dead zone, the local voltage regulation command is to lower the voltage.

[0118] If Qcharge > Qty, control the energy storage battery to charge by the difference between the two (absorbing reactive power), so that Qcharge′ = Qty; if Qcharge < Qty, control the energy storage battery to charge by the current maximum power Qchargemax (absorbing reactive power), and at the same time control the photovoltaic-energy storage converter and the photovoltaic MPPT tracker to limit power generation (limiting reactive power generation), so that Qchargemax + Qpv′ = Qty.

[0119] In the process of implementing voltage source control strategy in energy storage converter, since the voltage amplitude and phase angle have a certain maintenance capability, it can provide zero-delay synchronous reactive power compensation and short-term inertia support when the system fails. The effect is similar to that of the existing synchronous condenser, and it can realize the replacement of the synchronous condenser.

[0120] In order to fully utilize the supporting capabilities of voltage source type photovoltaic-storage converters, the photovoltaic-storage converters need to have a certain overload capacity. Typically, a short-term overload capacity of 3 times can meet the needs of most power grid scenarios. Special scenarios need to be determined based on the analysis of the access system.

[0121] The photovoltaic-storage converter uses the internal potential amplitude and phase angle as control targets, exhibiting autonomous voltage source characteristics. It provides a true voltage source to the grid connection point through the connection impedance, which can adapt to grids of different strengths and provide true inertia / synchronous voltage support for the grid.

[0122] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photovoltaic-storage integrated synchronous generator, characterized in that, It mainly includes photovoltaic MPPT trackers, energy storage batteries, photovoltaic-energy storage converters, coordination controllers, and step-up transformers; A photovoltaic MPPT tracker is used to connect a photovoltaic string to a DC bus, enabling the photovoltaic string to operate at maximum power. The energy storage battery is directly connected to the DC bus; Photovoltaic-storage converters are used to realize three-way energy conversion and voltage source active support control between photovoltaic MPPT trackers, energy storage batteries and AC grids; A step-up transformer is used to connect the photovoltaic-storage converter to the AC power grid; The coordinating controller receives scheduling instructions from the station control layer and controls the photovoltaic-storage converter and photovoltaic MPPT downwards, controlling the combined grid connection of photovoltaic and storage according to different scheduling instructions.

2. The integrated photovoltaic-storage synchronous generator according to claim 1, characterized in that, A current transformer and a voltage transformer are installed between the photovoltaic energy storage converter and the step-up transformer to collect the output current and voltage signals of the photovoltaic energy storage converter and transmit them to the coordination controller.

3. The integrated photovoltaic-storage synchronous generator according to claim 1, characterized in that, The coordinating controller communicates with the energy storage battery, the photovoltaic MPPT tracker, and the photovoltaic-energy storage converter. It determines whether the energy storage system is ready for charging / discharging based on the state of charge of the energy storage battery. It utilizes the power difference between the photovoltaic DC side power and the AC grid connection point to achieve charging / discharging control of the energy storage battery.

4. The photovoltaic-storage integrated synchronous generator according to any one of claims 1 to 3, characterized in that, The coordinating controller collects real-time output data from the photovoltaic-storage converter, photovoltaic MPPT, energy storage battery, and low-voltage side power output data from the step-up transformer, and uploads it to the monitoring system.

5. The integrated photovoltaic-storage synchronous generator according to claim 1, characterized in that, The rotor equation of the synchronous generator is: Where Tm and Te are the mechanical torque and electromagnetic torque of the synchronous generator, respectively, in N·m; ω and ω0 are the actual angular velocity of the power grid and the synchronous angular velocity, respectively, in rad / s; D is the damping coefficient, in N·m·s / rad; Pm is the mechanical power of the synchronous motor, Pe is the electromagnetic power of the synchronous motor; J is the moment of inertia, in kg·m2; and δ is the output power angle, in rad.

6. The integrated photovoltaic-storage synchronous generator according to claim 1, characterized in that, The photovoltaic-storage converter adopts a voltage source control strategy, and the mathematical models used for the active and reactive power loops are as follows: θ=∫ωdt (3) In equations (1)-(3), P* and Q* are the reference values ​​of the output active and reactive power, respectively; P and Q are the feedback values ​​of the output active and reactive power, respectively; Dp is the damping coefficient; Dq is the reactive-voltage droop coefficient; ω* and ω are the rated and actual values ​​of the grid electrical angular velocity, respectively; J is the virtual moment of inertia; K is the inertia coefficient of the simulated excitation regulation; Ug* and Ug are the rated and feedback values ​​of the grid voltage amplitude, respectively; E and θ are the amplitude and phase of the output potential, respectively.

7. A photovoltaic-storage integrated synchronous power generation system, characterized in that, Includes at least two photovoltaic-storage integrated synchronous generators as described in any one of claims 1 to 6; Each photovoltaic-storage integrated synchronous generator includes an energy storage battery, a photovoltaic-storage converter, a coordination controller, and several photovoltaic MPPT trackers; Each photovoltaic MPPT tracker is connected to at least one photovoltaic string; The photovoltaic-storage integrated synchronous generator system also includes a station control layer monitoring system, a fast power control system, and a cluster coordination control system; The monitoring system, the fast power control system, and the cluster coordination control system are respectively connected to the coordination controller of each integrated photovoltaic-storage synchronous generator.

8. The photovoltaic-storage integrated synchronous power generation system according to claim 7, characterized in that, The monitoring system includes an automatic power generation control system and an automatic voltage control system.

9. A method for joint control of photovoltaic and energy storage, characterized in that, Applied to a photovoltaic-storage integrated synchronous power generation system as described in claim 7 or 8, the method includes: The rotor motion equation of a synchronous generator is simulated using a voltage source controlled photovoltaic energy storage converter. The energy to maintain the rotational inertia of the simulated rotor is provided by a storage battery directly connected to the DC bus.

10. The photovoltaic-storage joint control method according to claim 9, characterized in that, The coordination controller is connected to the station control layer's monitoring system, fast power control system, and cluster coordination control system. The coordination controller selects between remote mode and local mode based on instructions from the monitoring system.

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